1. Field of the Invention
The present invention relates generally to arc welding, and more particularly to a method of vertically upward arc welding for vertical and inclined joints.
2. Description of the Prior Art
As the conventional method of high efficiency welding of vertical joints, there are known various methods, such as electroslag welding, electrogas welding and consumable nozzle electroslag welding methods, and these methods have been employed in the art. In each of these known welding methods, since a groove gap is necessary, the sectional area of the groove is large, resulting in disadvantages such as excessive heat input and relatively low welding speed. Accordingly, problems are left unsolved as regards the welding efficiency and the toughness of the heat-affected zone.
Recently, as a means of overcoming the foregoing disadvantages of the conventional welding methos, there has been proposed a vertical welding method in which a small diameter wire electrode is oscillated and welding is conducted in an atmosphere of carbon dioxide gas and/or other inert gases, and this method is practiced in some plants. However, since the diameter of the wire is small, when thick plates are welded, it is necessary to weave the wire or to move the wire back and forth in the direction of the plate thickness, as disclosed in Japanese patent publications Nos. 9857/70, and 50504/72, and because of the use of a small diameter wire, the applied welding current is low and since the penetration depth is shallow, if a groove gap is not sufficiently provided, no reverse bead is formed, and the lack of fusion may occur. Furthermore, since a groove gap is necessary, the sectional area of the groove is increased and a large heat input is necessary. Accordingly, the problem of a low welding speed is not solved. Moreover, since the penetration depth is shallow, there is brought about the disadvantage that the allowable range of the groove accuracy is very narrow.
Japanese Patent application laid-open specification No. 93240/74 proposes a narrow groove vertical welding method in which a strip electrode is inserted along the bisectional plane of an I-shaped groove gap. According to this method, it is impossible to generate an arc from the electrode to an upper base metal disposed above the surface of a molten pool or to melt the upper base metal over a sliding backing shoe on the front surface side of the groove. Accordingly, this method cannot be accurately applied to the welding of a narrow groove.
Still further, Japanese patent application laid-open specification No. 96945/74 discloses a vertically upward welding method using a strip electrode. According to this method, the strip electrode is fed with an inclination of a certain angle with respect to the weld line in compliance with the inclination of a welding crater. This method is characterized in that a relatively small current is used and slagging of a molten metal to the front side of the groove is prevented by the arc force of the inclined strip electrode. Accordingly, this method involves a problem that high-speed high-efficiency welding using the large current is impossible.